What are three requirements to perform an in-service software upgrade (ISSU)?

What are three requirements to perform an in-service software upgrade (ISSU)? Choose three.

A.
The device must have dual Routing Engines.

B.
Nonstop active routing (NSR) must be disabled.

C.
The command request system software issue add must be used to upgrade the software.

D.
The master and backup Routing Engines must be running the same software release.

E.
Graceful Routing Engine switchover (GRES) must be enabled.

Explanation: